The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In a video data compression apparatus, intra coding achieves efficient compression by performing transform, quantization, and entropy encoding on a residual signal obtained by efficiently removing spatial redundancy from a frame or block.
Representative examples of intra coding may include Joint Photographic coding Experts Group (JPEG) that is compression technique based on a block-wise Discrete Cosine Transform (DCT), and JPEG2000 that increases coding efficiency through an arithmetic coding technique based on Wavelet. It is known that intra coding technique using direction-based extrapolation prediction of H.264/AVC has the most excellent performance.
As shown in FIG. 1, the intra coding through direction-based prediction of H.264/AVC performs extrapolation prediction by using left and upper pixels A to M, of which encoding/decoding has been completed based on nine directions, including DC prediction (mode 2). That is, extrapolation prediction of a pixel value within a block is performed by filling the block with values taken from the left and upper pixels along prediction directions. For example, in the case of mode 0, extrapolation prediction is performed in a vertical direction, which has a 4×4 block of FIG. 1 filled with values of its upper pixels A, B, C, and D in arrow directions.
However, when a block to be encoded corresponds to a complicated texture area or a spatial gradient between pixels which is caused by light, spatial redundancy may not be efficiently removed during intra coding. In order to effectively solve this problem, an improved prediction technique has been proposed to compose a single pixel value to be predicted during extrapolation prediction with a combination of two or more adjacent pixels. However, this technique has a factor to limit the improvement of prediction performance by leaving a residual signal with respect to a block having only one principal edge.